The friction coupling comprises a set of coupling plates which are alternately, in a rotationally fast and axially displaceable way, connected to the one and the other of two coupling parts which are rotatable relative to one another, and which rest against an axially fixed abutment disc and which can be loaded by an axially displaceable pressure disc. For this purpose, the actuator comprises two discs which are rotatable relative to one another, one of which is axially supported relative to a fixed housing and the other one of which is axially displaceable. In their end faces facing one another, the two discs comprise ball grooves whose pitches extend in opposite directions. Each two opposed ball grooves which extend in opposite directions form a pair each of which accommodates a ball via which the discs are axially supported. The depth of each pair of ball grooves is variable around the circumference, so that a rotation of the discs relative to one another leads to the multi-plate coupling being axially displaced and thus actuated.
From WO 2005/035294 A1 there is known a drive assembly of a motor vehicle with two driven axles which can each be connected via a friction coupling to an output shaft of the manual gearbox. For actuating the friction couplings, an actuator system is provided which comprises two driven ball screw drives. The ball screw drives each comprise a nut and a spindle of which one component is operatively connected to an associated plate package. The transmission of force from the nut and spindle, respectively, to the plate package is effected via an intermediate axial bearing and spring.
U.S. Publication No. 2006/213747 proposes an axial setting device in the form of a ball ramp assembly which comprises a plate spring transmission wherein there is provided a first pressure plate which is acted upon by the axially displaceable disc of the ball ramp assembly, as well as a second pressure plate which loads the friction coupling. Between the two pressure plates, a plate spring is arranged which is incorporated in such a way that, by a lever effect, force is transmitted from the first to the second pressure plate.
DE 41 11 296 describes an axial setting device in the form of a ball ramp assembly for a friction coupling. Between the axially displaceable disc and the plate package, a needle bearing, a ring and a pressure pin are axially arranged in series. To return the axially displaceable disc, a plate spring is provided functionally in parallel thereto, which plate spring is located between the ring and the coupling carrier.
To control the driving dynamics of a motor vehicle so as to meet existing requirements, it is desirable to have very fine control of the respective friction coupling. Different heat expansion coefficients of the coupling components can lead to a changed reaction behavior of the friction coupling. Present friction coupling assemblies do not adequately address the effect of thermal expansion on the behavior of the coupling. Thus, there is a need for an improved coupling.